The first gay weddings could take place in just over a year's time after the Government detailed its plans to legalise same-sex marriages.
But the planned legislation will make it illegal for the Church of England or Church in Wales to marry gay couples.
The measures immediately came in for fierce criticism from Conservative traditionalists, who told Maria Miller, the Equalities Minister, that the Government had no mandate to drive through such a fundamental social reform.
On the other side of the debate, liberal church figures and Labour MPs were dismayed that the Government had so firmly shut the door on the prospect of gay marriages taking place in churches. The equal marriage legislation will now be published in January, with the intention of it pushing it through Parliament by next summer. The first same-sex weddings could take place in early 2014.
Deputy Prime Minister Nick Clegg told i: "We're now within a whisker of equal marriage rights for all couples – gay or straight. That's a big shift, totemic and profound."
More than 100 Tories – including several ministers – are expected to vote against the move, although party sources insisted the majority of its MPs would support the reform. It will be backed by overwhelming numbers of Liberal Democrat and Labour MPs.
MP Brian Binley has accused Mr Cameron of failing to chime with the party's instincts. He said: "Countless activists are feeling driven to give up their much-needed support for the party and, as any legislation progresses, this can only get worse."
In an effort to placate Tory backbenchers and faith groups, Ms Miller unveiled a planned "quadruple lock". Her legislation will state explicitly that no religious organisation – or minister – can be forced to marry same-sex couples. It will also make it unlawful for ceremonies to be staged unless the faith groups conducting them have chosen to do so.
The Equality Act will be amended to ensure discrimination claims cannot be brought against individuals or organisations that will not marry homosexuals. In the surprise fourth move, the legislation will specify that it will be illegal for the Church of England or Church in Wales to stage same-sex wedding ceremonies.